Mouse Estrous Cycle

Stage Ovary Uterus Vagina Smear
Diestrus Small follicles only are present with large corpora lutea from the previous ovulation. These secrete for only a very short time unless pregnancy or pseudopregnancy intervene. Small and anaemic, low motility, lumen small and slit-like. Cells of the uterine mucosa columnar; polymorphonuclear leucocytes in stroma; endometrial glands collapsed, atrophic. Epithelium thin, mitotic figures infrequent. Leucocytes abundant in stroma, migrate through the epithelium into vaginal lumen. Stringy mucous in which are entangled many leucocytes and a few nucleated epithelial cells.
Proestrus Some follicles grow rapidly. Become more vascular, water content increases, organ distends. Contractility more pronounced. Epithelial cells become higher (continuing into estrus). Leucocytes disappear from mucosa. Endometrial glands hypertrophy. Epithelum thickens, numerous mitoses in inner layers. Old layers of epithelium line the lumen. Leucocytes no longer migrate through the epithelium. Superficial epithelial cells slough off into lumen. Largely small, round, nucleated epithelial cells, singly or in sheets. None to few leucoytes.
Estrus Ovulation in the rat is spontaneous and occurs about 10 hours after the beginning of estrus. “Heat” (receptivity) lasts about 13 hours. Usually 10-20 eggs ovulated each time. gains maximum vascularisation. Epithelial cells reach maximum development. No leucocytes. Outer layer of epithelial cells become cornified and sloughed into the lumen. In early estrus these cells retain their nuclei, but in later stages no nuclei visible and the cells are irregular, flat, cornified plates. The skin around the vaginal orifice becomes swollen. Contains hundreds of large cornified cells (squames) with degenerate nuclei. Towards the end of estrus the smear becomes “cheesy” – masses of adherent cornified cells.
Metestrus Many corpora lutea, which secrete only for a very short time, and small follicles. Epithelium continues vacuolar degeneration and replacement. Leucocytes in stroma. Decrease in size and vascularity. Deeper layers of the estrous epithelium now line the lumen, the older, superficial layers having become cornified and sloughed off. Reduction of mitotic activity in epithelium. Leucocytes in stroma and migrating through the epithelium into the lumen. Many leucocytes and a few cornified cells